Radio communication



Jan. 12, 1937. H. H. BEVERAGE 2,067,432

' RADIO COMMUNICATION l Filed Dec. 5, 1923 2 Sheets-Sheet 1 Jan. 12,1937. H. H. BEVERAGE RADIO COMMUNICATION Filed Dec. 5, 1923 2Shees-Sheel 2 .MJNV

Patented Jan. 12, 1937 UNITED STATS PATENT OFFICE RADIO COMMUNICATION ofDelaware Application December 5, 19.28, Serial No. 323,809

1 Claim.

This invention relates to radio communica-tion, and more particularly toa method and means for reducing the effect of fading when communicatingon short waves.

To overcome the effect of fading when communicating on short Waves isthe primary object of my invention, and to this end I propose afrequency diversity method, which includes the transmission andreception of the same signal on several short wave carriers having onlyslightly different frequencies. It is not feasible to employ widelydifferent frequencies because the diurnal transmission characteristicsthen will differ, and during much of the day if one of the frequenciescomes through the others will not, so that instead of having a diversitysystem there will be only one channel in operation. Furthermore it isfar preferable to utilize slightly different high frequencies inaccordance with my invention because less space in the availablefrequency spectrum is needed for each channel. I propose, for example,

to use a difference of the order of magnitude of that between 16 and161/2 meters as a maximum, and, in the case of code signals, I nd thatit is satisfactory to use a difference as slight as an audiblefrequency, say 2 or 3 thousand cycles per second. In this manner thegeneral transmission characteristics are kept alike, but theinstantaneous fading characteristics may differ widely.

I find that not only does the fading at any instant of two waves ofslightly different high frequency continually Vary, but, consistentlytherewith, their relative phase also continually varies relative to thenormal variation due to frequency difference. It therefore would beimpossible to combine the radio frequency energies directly together,even if they were of the same frequency.

It therefore also is impossible to combine equal intermediate.frequencies together, after beating each of the received frequencieswith a different local oscillator frequency such that the intermediatefrequencies are equal, because the relative phase of the intermediatefrequency energies fluctuate just like that of the incoming radiofrequency energies, for if of two beating waves one is kept constant inphase, while the other is varied in phase, their beat is equally variedin phase. Now in accordance with my invention I overcome thesedifficulties by first rectifying the received energies, 0 and combiningthem only after rectification, so that the combination is substantiallyindependent of radio frequency phase.

In the case of code communication I may employ two transmitters ofdifferent frequency, and key them simultaneously. In such case bothtransmitters transmit during marking periods, and not during spacingperiods. As an alternative the transmitters may be keyed so that one istransmitting during marking periods, and not during spacing periods,While the other transmits during spacing periods, and not during markingperiods. This possesses the advantage of making it possible to employ asingle transmitter and to slightly detune the transmitter with thekeying means, in order to obtain a back wave for the spacing periods.

At the receiver the radiated energies are collected, amplifiedseparately or together, but, separately rectified, and then the markingenergy is utilized to actuate a translating device in one sense, and thespacing energy is used to actuate the same translating device in theopposite sense, so that both and also either of the marking and spacingenergies alone will produce a readable signal. To accomplish this effectin a very simple manner I reverse the phase of one of the rectifiedenergies, preferably by putting the energy through a three electrodetube, and then combine the rectified energies in additive phase andapply the combined energy to a single translating dev1ce.

My invention is described more particularly in the followingspecification, Which is accompanied by drawings in which Figure 1 is acode communication system arranged for simultaneous transmission of themarking periods; Figure 2 is a modification applicable to signalmodulation by speech or other speech-simulating signals; Figure 3 is anarrangement for alternate transmission of marking and spacing waves;Figure 4 is a section of tape explanatory of the operation of thearrangement shown in Fig. 3 Figure 5 is a system employing a singletransmitter arranged for keying with a back wave, and a preferred formof receiver; and Figure 6 is a portion of recording tape explanatory ofthe operation of the receiver shown in Figure 5.

Referring to Figure l there are a pair of transmitters 2 and 4, eachtuned to slightly different high frequencies, and each coupled to anantenna 6 and 8. Both transmitters are simultaneously keyed by a singlekeying means. which arrangement is schematically indicated by the keyI0. connected in parallel to both of the transmitters. The details ofthe keying connections are immaterial, and may be of any conventionaltype, such as those which establish a high negative or blocking bias onthe control electrode of one of the tubes in the transmitter.

The receiver cooperating with the transmitter shown in Figure 1 may beof simple form, comprising the antennas I2 and I4, and the amplifiers I6and I8, each tuned to the frequency of one of the radiated waves. Itshould be understood that the amplifiers IB and I8 may include autodyneor heterodyne stages, so that part or al1 of the amplification may beperformed at an intermediate instead of atthe original radio frequency.The amplified energies are fed to separate detectors 20 and 22, hereillustrated as full wave rectiflers, the .output from which may beamplified in amplifier tubes 24 and 26, and then combined in a commonrelay 28, which, in the case of a remotely located translating'device30, may be used to-key a tone generator 32 in order to transmit a tonesignal on the land line 34 in accordance with the received code signal.

If it is desired to transmit speech, or other Speech-simulating signals,such as modulation for multiplex code or picture work, a very similararrangement maybe employed, indicated in Figure 2, in which thetransmitters'Z and 4 are modulated, rather than keyed, in anyconventional manner, by a microphone or other source of modulatingenergy 36. The radiated energy is collected on antennas I2 and I4,amplified in amplifiers I6 and I8, rectified in rectiiiers 20 and 22,`to obtain the modulation energy, which then may be amplified inamplifier tubes 24 and 26, the outputs from which are combined in asingle impedance 38, coupled to an amplifying tube 48, the anode circuitenergy of which is fed, through a transformer 42, to any suitabletranslating device, here exemplified byv a loud speaker 54. 'Ihe twocarriers used in this scheme should differ sufficiently 4it preferableto so key the transmitters that one transmits during the markingperiods, while the other transmitsduring thespacing periods, and "sucharrangement' has been'illustrated in Figure 3. Referring to this figureit Will be seen that the transmitters 52, and 54, instead of beingcoupled to separate antennas, as in Figure l, are coupled to a singleantenna 56, but in this case the keying means 68 is arranged, as shown,to aifect the transmitters alternately, rather than simultaneously. Thereceiver, instead of employing separate -,a .nt ennasalso .hasa singleantenna 62, coupled 'to amplifiers 66 and 68, which in turn lead torectifiers 'IIJ and I2, the outputs from which may be amplified inamplifier tubes 'I4 and T6. However, the energies cannot then bedirectly combined t0- gether, as in Figure l, for they then act in thesame direction and no useful effect on the recorder would be obtainedinasmuch as they would add up to a constant value, and yield no signalat all. To obtain a signal these energies must be combineddifferentially, and this has been indiycated by the zero centerdifferential relay 8U, ywhich, is presumed to control a spring centeredcontacting arm which closes the circuit (if the common line 8| witheither the positively charged Y line 82, or the negatively charged line84, accord- ',ing to whichoi the receivers .is being energized 'by thetransmitter at that instant. The lines 82 a mean Zero line, both andalso either of the marking and spacing energies will produce a readableThis may be explained in connection with Figure 4, indicatingfragmentary portions of a recording tape obtained from the translator 86in Figure 3. Referring to Figure 4 it will be seen that relative to amean zero line, when one of the signalling energies, say the spacingenergy, fades, and the marking energy does not, a tape will be obtainedshowing the desired signal above the zero line, as is indicated at 98. If, on the other hand, the marking energy should fade, while the spacingenergy does not, a signal will be obtained below the Zero line, butreadable with respect to its own lower base line, as is indicated at 92.However, should neither fade, a signal of amplified strength will beobtained, ranging between the extremes of the negative flow produced bythe spacing Wave, and the positive flow produced by the marking wave, asis indicated at 94. Except in the event of simultaneous fading of bothYthe marking and spacing energies, a readable signal will always beproduced.

In Figure 3"the transmission system utilizes separate transmitters, butone is worked While the other is not. Only one being worked at a timesuggests the possibility ofusing a single transmitter keyedwith abackWave, and such an arrangement isA shown in Figure.5. Referring to thatfigure there is a tube |00, the anode to cathode and control electrodeto cathode circuits of which are regeneratively coupled by the coils |82and |84, which are tuned'by a tuning condenser |86. Direct anode andcontrol electrode bias potentials are applied througlf'the leads |88 andI II) to either side of the blocking condensers VI I2 and I I4; Theoutput of this oscillator may be amplified in any suitable poweramplifier I I6, and radiated over an antenna system ||8. The oscillatoris so keyed as to change its transmission frequency slightly. Two simpleways to do this have been indicated, in one of Ywhich a key.|28 is usedto short circuit a portion of the 'inductance' of the resonant circuit,and in the' other of which a key |22 is used to vary the spacing of asmall condenser I24, which is connected in parallel 'with the maintuning condenser |86. By thesek or any i other suitable frequencyvarying schemes a single transmitter may be employed in place of the twotransmitters indicatedin Figure3.

The receiver shown in Figure 5 comprises an antenna |38, the energycollected by which isamplified in a radio frequency amplifier |32, andthen heterodyned with energy from a local oscillator |34, ina'heterodyne detector |36, to' obtain intermediate frequency energy.This is readily separated into marking and spacing energies, by

the high pass filter |38 and the lowpass filter |48. The ltered energiesare also respectively amplied in intermediate frequency amplifiers |42and |44. The amplieroutputs.arerectified in suitabie remmers uis-analas, this rectified currents from which are passed throughlow passfilter sections |50 and |52, which serve to by-pass the radio frequencycomponents of the rectiedenergy, and to steady the rectified signalenergies.

One ofthe rectified energies is reversed in phasep preferablybypassingitthrough a three electrode -tube |54, coupled by asuitablefcoupling Vresistance |56, and the anode circuit of the tube |54is connectedto the anode circuit of the rectifier |48, as shown. Theanode of vthe tube |54 is polarized by a suitable source of direct anodepotential |58. The control electrode of the tube I 54 is biased from abias batteryl', in cooperation with a potentiometer resistance |62, andthe magnitude of the bias potential is so adjusted that itfwillbew75overcome or made sufficiently negative by incoming signal energy to stopanode current from flowing. With this adjustment the pen of thetranslating device |64 normally will remain at a value above the zeroaxis, assuming no keying, because of the steady anode current from thesource |58. Should one of the signals, say the marking signal, alonereach the receiver, and it be amplified and rectied in the units |44 and|48, the resulting rectified current will add to the steady anodecurrent from the source |58, and a readable signal will be obtainedabove the normal base. This has been indicated at |10 in Figure 6, inwhich the dotted line shows the normal position of the pen. Should themarking signal fade, and the spacing signal alone reach the receiver, itwill serve to negatively bias the tube |54, and so decrease its anodecurrent to zero, resulting in a readable signal such as has beenindicated at |12 in Figure 6. If both signals are received withoutfading, a signal of double amplitude is obtained, as is indicated at |14in Figure 6.

It should be understood that either of the transmitters indicated inFigures 3 and 5 may be used with either of the receivers shown inFigures 3 and 5. It should also be understood that in any of thereceivers the ampliers which precede the rectiers may include separateor combined heterodyne means followed by intermediate frequencyampliers. In code work the intermediate frequency may be as 10W as anaudio frequency. Also, any of the rectiers may be equipped with 10W passfilters, such as has been indicated in Figure 5. The single antennashown in Figure 3 may be used in connection with the other arrangementsillustrated in Figures 1 and 2, instead of separate antennas, owing tothe closeness of the two carrier frequencies. Full wave rectiers are notessential. More than two frequencies may be employed, if desired,particularly in the arrangements shown in Figures 1 and 2.

I claim:

An arrangement for reducing fading when transmitting code signals onshort Waves including a transmission system comprising a short wavetransmitter, keying means for slightly changing the frequency oftransmission to distinguish between marking and spacing periods, andmeans to radiate the marking and spacing energies alternately, and areceiving system comprising means to collect the radiated energies,separate electron emission tube amplifiers for the marking and spacingenergies, separate rectiers coupled to each of said ampliers, a threeelectrode tube coupled to the output circuit of one of the rectiiers forreversing the phase of the rectified energy, means coupling the anodecircuit of the three electrode tube With the output circuit of the otherrectifier so as to combine the marking and spacing energies in additivephase, and a translating device responsive to the combined energy.

HAROLD H. BEVERAGE.

